Solid drill bit for machine tools

ABSTRACT

The invention relates to a solid drill bit for machine tools. The solid drill bit has a drill bit body ( 10 ) and two indexable inserts ( 20, 22 ) which are arranged at a radial distance from one another in a respective insert seat ( 16, 18 ) of the drill bit body ( 10 ) in the region of a chip flute ( 12, 14 ). The indexable inserts ( 20, 22 ) have an essentially quadratic contour. They project with their front-end main cutting edges ( 30, 34 ) axially beyond the drill bit body ( 10 ) and overlap one another radially in their active region. The radially outer indexable insert ( 22 ), with its outer insert corner ( 36 ) and with its adjoining secondary cutting edges ( 38 ) perpendicular to the relevant main cutting edge ( 34 ), projects radially beyond the circumference of the drill bit body. In order to permit burr-free through-drilling, the front-end main cutting edge ( 34 ) of the outer insert ( 22 ) is subdivided in its longitudinal extent into a radially inner working section ( 50 ) and a rectilinear peeling section ( 52 ) adjoining said working section ( 50 ) on the outside and extending up to the outer insert corner ( 36 ), said sections ( 50  and  52 ) enclosing a setting angle of 95° to 120° with one another. In the fitted state, the peeling section ( 52 ), toward the outer insert corner ( 36 ), is accordingly set at a positive setting angle of 72° to 87° relative to the end face of the drill bit body.

The invention relates to a solid drill bit for machine tools, having adrill bit body and at least two inserts which are arranged at a radialdistance from one another in a respective insert seat of the drill bitbody in the region of a chip flute, project with their front-end maincutting edges axially beyond the drill bit body and radially overlap oneanother in their active regions, the radially outermost insert, with itsouter insert corner, which forms a diameter, and its adjoining secondarycutting edge, projecting radially beyond the drill bit body, and thesecondary cutting edge, starting from the insert corner, being inclinedat a defined setting angle in its longitudinal extent in the directionof the drill bit body.

Drilling tools of this type having two essentially quadratic indexableinserts are known (WO01/85375). The two quadratic inserts are arrangedat different radial distances from one another. With their front-endmain cutting edges, they project with a positive rake angle axiallybeyond the drill bit body. The inner insert has a pre-cutting action inthe axial direction, the distance corresponding approximately to theradius of curvature in the region of the insert corners. The inclinationof the secondary cutting edge of the outermost insert, at less than3.2°, is selected in such a way that the secondary cutting edge forms aguide edge which, during the drilling operation, under the effect of adrifting force pointing radially outward, bears in a sliding manner, atleast over part of its length, against the wall of the hole producedbeforehand. When drilling through workpieces of ductile material usingsuch solid drill bits, it has been found that a projecting burr isformed from the hole in the radius region, this burr often having to beremoved subsequently. Burrs also occur during the spot drilling withsuch a solid drill bit. Tests have shown that, even by using insertshaving rounded-off insert corners, a burr formation cannot be avoided.

Based thereon, the object of the invention is to improve the known soliddrill bit and its inserts to the effect that burr-free through-drillingis possible even in workpieces of ductile material.

To achieve this object, the feature combinations specified in patentclaims 1 and 9 are proposed. Advantageous configurations anddevelopments of the invention follow from the dependent claims.

The solution according to the invention is based on the idea ofdesigning the main cutting edge in such a way that a burr forming in thediameter region of the hole can be cut in the manner of a peeling orreaming operation. In order to achieve this, it is proposed according tothe invention that the front-end main cutting edge of the outer insertbe subdivided in its longitudinal extent into a radially inner workingsection and a rectilinear peeling section adjoining said working sectionon the outside and extending up to the outer insert corner, saidsections enclosing an angle of 95° to 120° with one another. The workingsection leads during the drilling operation, while the peeling sectionfollows up in the diameter region with a steep peeling angle. As aresult, the workpiece in the vicinity of the diameter region, dependingon the steepness of the setting angle, is divided into more or less finemarginal chips, so that a burr formation is avoided.

A preferred configuration of the invention provides for the workingsection of the main cutting edge, toward the peeling section, to be setat a positive setting angle of 2° to 10° relative to the imaginary endface, perpendicular to the drill bit axis, of the drill bit body,whereas the peeling section of the main cutting edge, toward the outerinsert corner, is set at a positive setting angle of 77° to 87° relativeto the end face of the drill bit body. The transition point betweenworking section and peeling section of the main cutting edge may berounded off convexly. In contrast to that, the outer insert cornershould be of relatively sharp-edged design. In the region of the outerinsert corner, the peeling section of the main cutting edge and theadjacent secondary cutting edge enclose an angle of 160° to 175° withone another, the secondary cutting edge, in accordance with WO01/85375,being expediently inclined with a setting angle of less than 3.2° in thedirection of the drill bit body.

A further advantageous configuration of the invention provides for acentral section extending up to the inner insert corner to adjoin thepreferably rectilinear working section of the front-end main cuttingedge radially on the inside, this central section enclosing a sweepbackangle of 160° to 175° with the working section and being set at anegative setting angle of 3° to 18° relative to the end face of thedrill bit body. The active region of the central section of thefront-end main cutting edge of the outer insert is expedientlyoverlapped by the front-end main cutting edge of the inner insert. Thisis therefore important because the inserts are preferably designed asindexable inserts having four identical main cutting edges, the centralsection of a first main cutting edge, during an indexing operation,being turned into the peeling section of an adjacent main cutting edge.It is therefore important that the central section of the outer insertremains free of wear during the drilling operation.

The invention is explained in more detail below with reference to anexemplary embodiment shown schematically in the drawing, in which:

FIG. 1 shows a solid drill bit for machine tools with essentiallyquadratic indexable inserts in a diagrammatic illustration;

FIGS. 2 a to c show a plan view and two cut-away side views of the soliddrill bit according to FIG. 1;

FIG. 3 shows a plan view of an indexable insert in an enlargedillustration;

FIGS. 4 a and b shows two sectional illustrations along section linesA-A and B-B in FIG. 3.

The tool shown in the drawing is intended as a solid drill bit formachine tools. It has an essentially cylindrical drill bit body 10 whichis provided with two chip flutes 12, 14. A respective insert seat 16, 18for accommodating an essentially quadratic indexable insert 20, 22 isprovided at the front end of the chip flutes. The indexable inserts 20,22 are each fastened to the drill bit body 10 by a countersunk headscrew 26 which engages in a tapped hole 24 of the drill bit body 10.

As can be seen from FIGS. 2 a to c, the inner indexable insert 22, withthe inner insert corner 28 at its front-end main cutting edge 30,overlaps the drill axis 32, whereas the outer indexable insert 22, withits main cutting edge 34 in the region of the outer insert corner 36 andwith its outer secondary cutting edge 38, projects beyond thecircumference of the drill bit body 10. In addition, the indexableinserts, with their main and secondary cutting edges, are arranged so asto be tilted relative to the drill bit body 10 in such a way that themain cutting edges enclose a positive setting angle α_(i)=4° andα_(a)=2°, respectively, relative to a plane perpendicular to the drillaxis, the indices i and a identifying the inner and outer inserts,respectively. Since the secondary cutting edge 38 is orientedperpendicularly to the adjacent main cutting edge 34, the secondarycutting edge 38, in the exemplary embodiment shown, is inclined,starting from the insert corner 36, in its longitudinal extent in thedirection of the drill bit body at a setting angle which corresponds tothe angle α_(a). It can also be seen from FIG. 2 a that the main cuttingedge 34 of the outer indexable insert 22, in the direction of rotation,indicated by the arrow 40, about the drill axis 32, encloses with themain cutting edge 30 of the inner indexable insert 20 an angle which issmaller than 180° by the angle β. In the exemplary embodiment shown, theangle β is about 5°. Finally, it can be seen from FIG. 2 b that the maincutting edge 30 of the inner indexable insert 20 is at a pre-cuttingdistance d in front of the main cutting edge 34 of the outer indexableinsert 22, this distance d being 0.23 mm in the exemplary embodimentshown. The angles α_(i), α_(a) and β and the pre-cutting distance d areselected in such a way that the drill, with a defined, radial driftingforce, in the region of its outer secondary cutting edge 38, bears in asliding manner against the wall 42 of the produced hole.

As can be seen in particular from FIG. 3 in conjunction with FIG. 2 b,the main cutting edges 34 of the indexable inserts 22 are subdivided intheir longitudinal extent into a rectilinear working section 50 and anadjoining, rectilinear peeling section 52 extending up to the firstinsert corner 36, said sections 50 and 52, in the exemplary embodimentshown, enclosing an angle of 105° with one another in the region oftheir rounded-off transition point 54. The peeling section 52 of themain cutting edge 34 and the adjacent secondary cutting edge 38 enclosean angle of 165° with one another. Adjoining the rectilinear workingsection 50 of each main cutting edge 34 is a central section 58 whichextends up to the second insert corner 56 and encloses with the workingsection a sweepback angle 60 of 165°. The central section 58 of a firstmain cutting edge 34 has the function of a peeling section 52 uponindexing to the next main cutting edge 34.

At the outer insert 22, the subdivision of the main cutting edge 34 intothe working section 50 and the peeling section 52 has an importantfunction, which in addition is essential to the invention. This isbecause it has been found that, during conventional use of a maincutting edge 34 having an insert corner rounded off toward the secondarycutting edge 38 without peeling section 52, an undesirable burrformation occurs, in particular when drilling through ductileworkpieces. The burrs must be removed, for example filed off, in anadditional operation. The steeply running, rectilinear peeling section52 according to the invention, adjoining the working section 50 on theoutside, ensures that stock is removed from the workpiece in a peelingmanner in the diameter region while forming small chips. As a result, aburr formation is effectively avoided. The central section 58, set backat the sweepback angle, of the outer insert 22 is overlapped by the maincutting edge 30 of the leading inner insert 20 during the drillingoperation and is thereby rendered ineffective. This is necessary so thatthe central section 58, which becomes the peeling section 52 when theinsert 22 is indexed to the next main cutting edge 34, is not subjectedto any wear during the drilling operation.

It is possible in principle to also use the same inserts as innerinserts 20. In this case, dividing of chips, which is advantageous forthe drilling operation, occurs in the region of the sweepback anglebetween working section 50 and central section 58.

In summary, the following can be emphasized: the invention relates to asolid drill bit for machine tools. The solid drill bit has a drill bitbody 10 and two indexable inserts 20, 22 arranged at a radial distancefrom one another in a respective insert seat 16, 18 of the drill bitbody 10 in the region of a chip flute 12, 14. The indexable inserts 20,22 have an essentially quadratic contour. They project with theirfront-end main cutting edges 30, 34 axially beyond the drill bit body 10and overlap one another radially in their active region. The radiallyouter indexable insert 22, with its outer insert corner 36 and with itsadjoining secondary cutting edges 38 perpendicular to the relevant maincutting edge 34, projects radially beyond the circumference of the drillbit body. In order to permit burr-free through-drilling, the front-endmain cutting edge 34 of the outer insert 22 is subdivided in itslongitudinal extent into a radially inner working section 50 and arectilinear peeling section 52 adjoining said working section 50 on theoutside and extending up to the outer insert corner 36, said sections 50and 52 enclosing a setting angle of 95° to 120° with one another. In thefitted state, the peeling section 52, toward the outer insert corner 36,is accordingly set at a positive setting angle of 72° to 87° relative tothe end face of the drill bit body.

1. A drilling tool for machine tools, having a drill bit body (10) andat least two inserts (20, 22) which are arranged at a radial distancefrom one another in an insert seat (16, 18) of the drill bit body (10)in the region of a chip flute (12, 14), project with their front-endmain cutting edges (30, 34) axially beyond the drill bit body (10) andradially overlap one another in their active regions, the radially outerinsert (22), with its outer insert corner (36) and its adjoiningsecondary cutting edge (38), projecting beyond the drill bit body (10),and the secondary cutting edge (38), starting from the insert corner(36), being inclined at a defined setting angle (α_(a)) in itslongitudinal extent in the direction of the drill bit body,characterized in that the front-end main cutting edge (34) of the outerinsert (22) is subdivided in its longitudinal extent into a radiallyinner working section (50) and a peeling section (52) adjoining saidworking section (50) on the outside and extending up to the outer insertcorner (36), said sections (50, 52) enclosing an angle of 95° to 110°with one another.
 2. The drilling tool as claimed in claim 1,characterized in that the working section (50) of the main cutting edge(34), toward the peeling section (52), is set at a positive settingangle of 2° to 10° relative to the end face of the drill bit body. 3.The drilling tool as claimed in claim 1, characterized in that thepeeling section (52) of the main cutting edge (34), toward the outerinsert corner, is set at a positive setting angle of 72° to 87° relativeto the end face of the drill bit body (10).
 4. The drilling tool asclaimed in claim 1, characterized in that the transition point (54)between working section (50) and peeling section (52) of the maincutting edge (34) is rounded off convexly.
 5. The drilling tool asclaimed in claim 1, characterized in that, in the region of the outerinsert corner (36), the peeling section (52) of the main cutting edge(34) and the adjacent secondary cutting edge (38) enclose an angle of160° to 175° with one another.
 6. The drilling tool as claimed in claim1, characterized in that a central section (58) extending up to theinner insert corner (56) adjoins the rectilinear working section (50) ofthe front-end main cutting edge (34) radially on the inside, thiscentral section (58) enclosing a sweepback angle of 160° to 175° withthe working section (50) and being set at a negative setting angle of 3°to 18° relative to the end face of the drill bit body (10).
 7. The soliddrill bit as claimed in claim 6, characterized in that the active regionof the central section (58) of the front-end main cutting edge (34) ofthe outer insert (22) is overlapped by the front-end main cutting edge(30) of the inner insert (20) and is rendered ineffective.
 8. The soliddrill as claimed in claim 1, characterized in that the inserts (20, 22)are designed as indexable inserts having four main cutting edges (30,34) of the same length.
 9. An insert for a drilling tool which can beused in a machine tool, having at least one main cutting edge (30, 34),extending between a first and a second insert corner (36, 56), and asecondary cutting edge (38) adjoining the first insert corner (36),characterized in that the main cutting edge (30, 34) is subdivided inits longitudinal extent into a rectilinear working section (50) and anadjoining rectilinear peeling section (52) extending up to the firstinsert corner (36), said sections (50, 52) enclosing an angle of 95° to110° with one another.
 10. The insert as claimed in claim 9,characterized in that the transition point between the working section(50) and the peeling section (52) of the main cutting edge (30, 34) isrounded off convexly.
 11. The insert as claimed in claim 9,characterized in that, in the region of the first insert corner (36),the peeling section (52) of the main cutting edge (30, 34) and theadjacent secondary cutting edge (38) enclose an angle of 160° to 175°with one another.
 12. The insert as claimed in claim 9, characterized inthat a central section (58) extending up to the second insert corner(56) adjoins the rectilinear working section (50) of the main cuttingedge (30, 34), this central section (58) enclosing a sweepback angle of160° to 175° with the working section (50).
 13. The insert as claimed inclaim 9, characterized in that it is designed as an indexable insert(20, 22) having four insert corners (36) and four identical main cuttingedges (30, 34) which are offset from one another by 90° and of which ineach case the main cutting edge (30, 34) adjoining a first insert corner(36) at the same time performs the function of the secondary cuttingedge (38) with regard to the adjacent main cutting edge (30, 34) via therelevant insert corner (36).